1. Field of Invention
This invention relates generally to apparatus for controlling the operation of a stop sign on a school bus, and more particularly to a control apparatus that when the door of the bus is opened to unload or load passengers causes the stop sign to swing out to an outstretched position to provide a signal alerting nearby vehicles, and when the bus door is closed, then causes the sign to return to its retracted position.
2. Status of Prior Art
School buses serve to pick up or discharge children attending a school at various points along a route running through the community in which the school is situated. As a safety measure, school buses have for many years been equipped with a stop sign mechanism under the control of the bus driver. This mechanism acts to swing out the stop sign from its normally retracted position against the side of the bus to an outstretched position, thereby providing a signal alerting drivers of nearby vehicles that children are entering or alighting the bus.
U.S. Pat. Nos. 2,384,689 and 3,094,683 are illustrative of manually-operated school bus sign devices, while U.S. Pat. No. 2,252,529 discloses a hydraulically-operated school bus sign.
It is also known to provide motor-operated school bus signals, such apparatus being illustrated in U.S. Pat. Nos. 2,281,717 and 4,138,668. Of greatest prior art interest in this regard is the 1982 U.S. Pat. No. 4,339,744 to Latta, Jr. In this patent, the stop sign mounted on the side of the bus is operated by a unidirectional DC motor and a linkage associated with the sign. This linkage in conjunction with limit switches acts to deploy and retract the stop sign.
The control apparatus disclosed in the Latta et al. patent is operated by the driver by means of a switch having a "deploy" and a "retract" position. The arrangement is such that when the driver sets the switch to its "deploy" position, this also acts to actuate sign lights and bus lights to cause them to flash. These flashing light signals in combination with the outstretched stop sign warn nearby cars that the door of the school bus is then open and children are being loaded or unloaded.
One practical drawback of the Latta et al. stop sign control apparatus is that it is driver operated. Should the bus driver, as sometimes occurs, fail to operate the stop sign switch before opening the door, no warning signal will then be given to alert nearby car drivers. A school bus driver's job is made difficult by the fact that his young passengers are not always well behaved; for school children are often noisy and hyperactive. Hence the conditions which prevail in a bus may distract a bus driver and induce him to forget to operate the stop sign.
Another practical drawback of the Latta et al. stop sign is that it can be damaged or rendered inoperative if the outstretched stop sign is not made to retract by the motor linked thereto but is forced to retract either accidentally or deliberately while the motor is cut off. This action may break the linkage between the stop sign and the motor.
To overcome these drawbacks, the control apparatus disclosed in my copending application, above-identified, us automatically responsive to the opening and closing of the bus door, whereby when the door is opened, the control apparatus then acts to swing out the stop sign to its outstretched position; and when the door is closed, the apparatus then acts to return the sign to its normally retracted position on the side of the bus body. In this control arrangement, a unidirectional motor is operatively coupled to the hinged stop sign through an eccentric drive and link arm. The link arm is associated with limit switches so that in the course of a motor operating cycle the sign is swung to its outstretched position and then returned to its normally retracted position.
In order to prevent damage to the mechanism should an unauthorized attempt be made to forcibly retract the outstretched stop sign, in my prior control apparatus, a breakaway coupling is provided between the link arm operated by the motor and the shaft of the hinge mechanism for the sign. The breakaway coupling which is constituted by several components includes a spring and a cammed sleeve which act when the stop sign is improperly forced to retract, to decouple the stop sign hinge mechanism from the link arm to prevent damage to this arm and the electrical and mechanical components associated therewith.
While there are distinct advantages to be gained by the inclusion of the breakaway coupling in the control apparatus for the bus sign, because this coupling is relatively complex, it adds significantly to the cost of the control apparatus and makes assembly of the apparatus more difficult. Such cost factors play an important role in school bus purchases, for these are usually financed by local community taxes. Hence an automatic stop sign control apparatus for a school bus which is expensive may be ruled out by the community even though it affords an extra measure of safety.